Joint and Bone Disorders

Second last post! These last two will probably be relatively short.

What are the characteristics of osteoarthritis? Explain the difference between Heberden's and Bouchard's nodes.

Osteoarthritis is essentially a disease of "wear and tear." Repeated stress at the articular cartilage, from overuse of the joint or whatever, can wear away the cartilage, exposing the bone underneath. This can cause local inflammation inside the joint (as opposed to the systemic inflammation of rheumatoid arthritis), leading to narrowing of the joint. Another characteristic of osteoarthritis is the formation of osteophytes, or "bone spurs," inside the joint.

Signs and symptoms of osteoarthritis include pain, limited mobility and crepitus. Pain and limited mobility can lead to disuse of the joint, which can in turn lead to muscle atrophy. Another sign of osteoarthritis is the formation of hardened lumps, or nodes. Nodes in the distal phalanx (of the finger) are known as Heberden's nodes, whereas nodes in the proximal phalanx are known as Bouchard's nodes.

Treatments for osteoarthritis include rest (so as not to put more stress on the joint), glucocorticoids (to reduce inflammation), analgesics (to alleviate pain) and, if severe, joint replacement.

Why do rickets and osteomalacia occur? What is the difference between these two conditions?

Rickets and osteomalacia are conditions in which there is insufficient bone mineralisation. This is often due to a vitamin D deficiency (remember, vitamin D helps out with absorption of calcium and phosphate), which in turn may be due to malabsorption of these nutrients or renal disease (as vitamin D is activated by the kidneys). The difference between the two is the age at which they occur. Rickets occurs in children, and may lead to bowed (curved) legs that may stay that way for life if the condition is untreated. Osteomalacia occurs in adults whose bones have already formed, so bowed legs are generally not seen here.

Describe the characteristics of osteoporosis. What are some of the treatments that are commonly used?

Osteoporosis is a condition where there is not only insufficient mineralisation, but also insufficient matrix formation. This results in a decrease in bone matrix and bone density, especially in cancellous bone. People with osteoporosis are more at risk of compression fractures between vertebrae, at the femoral neck and so on, as well as spinal abnormalities such as kyphosis ("hunchback").

Primary osteoporosis, which is osteoporosis that isn't caused by another condition, is often seen in older adults, especially women. I have explained why this is so here. Secondary osteoporosis is osteoporosis due to another condition, such as Cushing's disease (the excess cortisol eats up the matrix), malabsorption and hyperparathyroidism. Other risk factors include decreased mobility, poor diet, smoking, caffeine and some drugs such as glucocorticoids, antacids (particularly those containing aluminium) and chemotherapy.

One of the main treatments for osteoporosis is supplementation of calcium and vitamin D. Exercise is also important in maintaining bone density. Bisphosphonates, which are molecules that resemble a double phosphate, may be used as they are less easily broken down by osteoclasts. Other drugs that may be used include oestrogen receptor modulators (SERMs), which increase oestrogen activity in bone but not in the reproductive tract (so as not to increase the risk of reproductive tract cancers); calcitonin, which opposes parathyroid hormone; and strontium ranelate, which acts as a calcium analogue that can increase the activity of OPG.

One more post to go!